The present invention relates to polishing pads for chemical mechanical planarization, and in particular, relates to porous polishing pads. Further, the present invention relates to apparatuses and methods for forming porous polishing pads formed from unexpanded microspheres.
In the fabrication of integrated circuits and other electronic devices, multiple layers of conducting, semiconducting and dielectric materials are deposited on or removed from a surface of a semiconductor wafer. Thin layers of conducting, semiconducting, and dielectric materials may be deposited by a number of deposition techniques. Common deposition techniques in modern processing include physical vapor deposition (PVD), also known as sputtering, chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), and electrochemical plating (ECP).
As layers of materials are sequentially deposited and removed, the uppermost surface of the wafer becomes non-planar. Because subsequent semiconductor processing (e.g., metallization) requires the wafer to have a flat surface, the wafer needs to be planarized. Planarization is useful in removing undesired surface topography and surface defects, such as rough surfaces, agglomerated materials, crystal lattice damage, scratches, and contaminated layers or materials.
Chemical mechanical planarization, or chemical mechanical polishing (CMP), is a common technique used to planarize substrates, such as semiconductor wafers. In conventional CMP, a wafer is mounted on a carrier assembly and positioned in contact with a polishing pad in a CMP apparatus. The carrier assembly provides a controllable pressure to the wafer, pressing it against the polishing pad. The pad is moved (e.g., rotated) relative to the wafer by an external driving force. Simultaneously therewith, a chemical composition (“slurry”) or other polishing solution is provided between the wafer and the polishing pad. Thus, the wafer surface is polished and made planar by the chemical and mechanical action of the pad surface and slurry.
Hishiki, U.S. Pat. No. 6,837,781, discloses a polishing pad known in the art manufactured by a RIM process. The polishing pad of Hishiki is formed by dissolving an inert gas in a mixture of polyurethane to create porosity. Unfortunately, polishing pads of Hishiki have large variations in porosity and may cause unpredictable, and perhaps, detrimental, polishing performances from one polishing pad to the next. For example, Examples 1 and 2 in Table 2 (see cols. 11-12) provided polishing pads having an average cell diameter of 15 μm and 3 μm, respectively. Further, Examples 3 and 4 in Table 2 provided polishing pads having an average cell diameter of 30 μm and 150 μm, respectively. In other words, these polishing pads have variations in porosity of up to about 80 percent, which may detrimentally affect polishing performance. Moreover, these variations in porosity may negatively affect polishing performance within the pad itself.
Hence, what is needed is a polishing pad having improved polishing performance. Moreover, what is needed is an apparatus and an efficient method of forming a porous polishing pad having improved polishing performance.